基于改进U-Net的量子点STM图像分割

为提升量子点图像分割精度,降低特征识别误差,提出一种基于改进U-Net的量子点图像分割方法.首先,在预处理阶段,设计了以色彩通道为权值的灰度化算法,以提升后续分割效果.其次,在STM图像分割部分,在原始U-Net结构上引入中间过渡层以均衡网络各层特征.而后,建立数据集,并通过实验对比不同分割算法的精确度、召回率、F-measure.最后,将分割算法应用于量子点的特征识别,并测试了不同分割方式对应用的影响.实验结果显示,改进灰度化方法保留细节信息丰富,明显提升了量子点分割精度;改进U-Net的平均精确率、召回率、F-measure相较原始网络分别提升了13.83%、2.16%、8.13%.同时,实验数据表明由于分割精度的提升,量子点数量、纵横比等特征参数的识别更加精确.     

Temperature－Induced Switching－Over of the Luminescence Transitions in GaInNAs／GaAs Quantum Wells

Photoluminescence (PL) spectra of the GaInNAs/GaAs single quantum well (SQW) with different N compositions are carefully studied in a range of temperatures and excitation power densities. The anomalous S-shape temperature dependence of the PL peak is analysed based on the competition and switching-over between the peaks related to N-induced localized states and the peak related to interband excitonic recombination. It is found that with increasing N composition, the localized energy increases and the turning point of the S-shape temperature dependence occurs at higher temperature, where the localized carriers in the handrail states obtain enough thermal activation energy to be dissociated and delocalized. The rapid thermal annealing (RTA)effectively reduces the localized energy and causes a decrease of the switching-over temperature.     

GaAs基GaAsSb/GaInAs双层量子阱的发光

嵌入GaAs中的GaAsSb／GaInAs量子阱因其在1．3～1．5μm光通信波段发光的潜力而受到关注,我们研究了一系列MBE生长的GaAsSb／GaInAs量子阱样品的光致发光,发现所有样品在室温下都出现了一个较强的、波长在1．3μm附近的低能峰和一个较弱的高能峰。变温及变激发功率的荧光谱测量研究发现,高能峰只有在150K以上的测试条件下才能观测到,并且其相对强度随着温度的升高而增加,其调制光谱显示出第一类跃迁的特征。他们建立了理论模型,计算的结果支持将这一发光峰指派为GaInAs层内电子的基态与重空穴激发态间的跃迁,并与实验数据吻合得很好。同时初步讨论了改善1．3μm的低能峰发光的方法。     

A GaAs/GalnP dual junction solar cell grown by molecular beam epitaxy

We report the recent result of GaAs/GalnP dual-junction solar cells grown by all solid-state molecularbeam-epitaxy （MBE）. The device structure consists of a GaIn0.4sP homojunction grown epitaxially upon a GaAs homojunction, with an interconnected GaAs tunnel junction. A photovoltaic conversion efficiency of 27% under the AM1.5 globe light intensity is realized for a GaAs/GaInP dual-junction solar cell, while the efficiencies of 26% and 16.6% are reached for a GaAs bottom cell and a GaInP top cell, respectively. The energy loss mechanism of our GaAs/GalnP tandem dual-junction solar cells is discussed. It is demonstrated that the MBE-grown phosphide-containing Ⅲ-V compound semiconductor solar cell is very promising for achieving high energy conversion efficiency.     

高对比度、高均匀性材料GaAs/AlGaAs多量子阱空间光调制器

本文报道了GaAs/AlGaAs 多量子阱空间光调制器的最新研究进展。使用MBE生长了3英寸材料,其横向均匀性好于0.1%, 法布里-珀罗腔谐振波长变化小于0.9nm。利用调节层腐蚀进行调节以后,在6.7V调制电压下实现了102的对比度。理论和实验均表明,调节层腐蚀能够在在宽范围内调节平衡条件,从而实现多量子阱空间光调制器的高对比度。     

Transparent conducting indium-tin-oxide (ITO) film as full front electrode in III-V compound solar cell

The application of transparent conducting indium-tin-oxide (ITO) film as full front electrode replacing the conventional bus-bar metal electrode in III-V compound GaInP solar cell was proposed. A high-quality, non-rectifying contact between ITO and 10 nm N⁺-GaAs contact layer was formed, which is benefiting from a high carrier concentration of the terrilium-doped N⁺-GaAs layer, up to 2×10¹⁹ cm^-3. A good device performance of the GaInP solar cell with the ITO electrode was observed. This result indicates a great potential of transparent conducting films in the future fabrication of larger area flexible III-V solar cell.     

喷射共沉淀法制备纳米ZnFe_2O_4及其结构表征

对化学共沉淀法加以改进称为喷射共沉淀法。采用喷射共沉淀法制备了ZnFe2O4纳米粉末材料。采用XRD、SEM和TEM进行结构分析结果表明喷射共沉淀法制备的ZnFe2O4纳米粉末颗粒细小均匀形状完整。由于纳米尺寸效应的存在纳米ZnFe2O4粉末材料具有铁磁性。从流体力学角度分析了喷射共沉淀法中物质的输运和反应过程并解释了试验结果。认为喷射共沉淀法是一种较好的制备氧化物纳米粉末材料的方法。     

Indium bump array fabrication on small CMOS circuit for flip-chip bonding

We demonstrate a novel method for indium bump fabrication on a small CMOS circuit chip that is to be flip-chip bonded with a GaAs/AlGaAs multiple quantum well spatial light modulator.A chip holder with a via hole is used to coat the photoresist for indium bump lift-off.The 1000μm-wide photoresist edge bead around the circuit chip can be reduced to less than 500μm,which ensures the integrity of the indium bump array.64×64 indium arrays with 20μm-high,30μm-diameter bumps are successfully formed on a 5×6.5 mm~2 CMOS chip.     

小片CMOS驱动电路的倒装焊In柱阵列沉积

本文研究了在用于GaAs/AlGaAs多量子阱空间光调制器驱动电路小片芯片上进行In柱阵列沉积的方法。使用了带有中央通孔的甩胶套进行甩胶,可以将驱动电路小片上1000um宽的胶边减小至500um,有效保证了沉积In柱阵列的完整性。使用此方法,64x64,20um高,30um直径的In柱阵列能够完整沉积在5mmx6.5mm的CMOS驱动电路上。     

GaInNAs/GaAs量子阱的光致发光谱和光调制反射谱

研究了GaInNAs/GaAs多量子阱在不同温度和激发功率下的光致发光(PL)谱以及光调制反射(PR)谱.发现PL谱主发光峰的能量位置随温度的变化不满足Varshni关系,而是呈现出反常的S型温度依赖关系.进一步测量,特别是在较低的激发光功率密度下,发现有两个不同来源的发光峰,它们分别对应于氮引起的杂质束缚态和带间的激子复合发光.随温度变化,这两个发光峰相对强度发生变化,造成主峰(最强的峰)的位置发生切换,从而导致表观上的S型温度依赖关系.采用一个基于载流子热激发和出空过程的模型来解释氮杂质团簇引起的束缚态发光峰的温度依赖关系.